Restart openvpn service along with network restart

When a network service restarts, openvpn service should be restarted as well if it is enabled.

Because if the network is restarted, openvpn stops working (it will lost interface or address or something), so since openvpn service depends on network service, it should be restarted as well anytime networks restarts: WAN tab, LAN tab, Guest network, ...

This issue does not depend on openvpn module, yet the issue affects it a lot. If a user configures a custom VPN server/client in uCI and network is restarted, it would be affected as well. This is the reason to have this issue in controller in general, not in turris/foris-controller-openvpn-module>